Mitotic activities were examined in the tips of seminal roots in Zea mays (White Dent) with the conventional paraffin method in a series of continuous 10μm sections of longitudinal and/or transversal after dying with Haematoxylin-and/or Gentian Violet solution. Results obtained through microscopical examinations are as follows: 1) Location where the cells of epidermis, cortex and stele began to elongate were asymmertrical in both sides, so were the mitotic activities in the mitotic zone suggesting that these phenomena had some relationships with the rotation growth of root tips. 2) Mitotic activities terminated at 1, 400 μm from the root tips. They could be observed in all tissues of epidermis, cortex and stele and they activated most frequently in the range of 510-600μm from the root tips. 3) Mitotic ratios were calculated with the nnumber of dividing cells to total cells in dividing the sweep range of microscope into twelve sections of 30° each to count them more accurately and the data were subtotalled in two groups of half, longitudinal cylindrical sections of 100μm in length and it was found that mitotic rations of the two sections had reversed six times until the cease of mitotic activities to the distance of 1, 400μm from the root tips. This results imply again the imbalance of mitotic activities and their periodic movement in the root tissues. 4) Original cells of 10μm could enlarge to 12 to 15 times at 7mm from the root tips that implied the great force of hormonal substances concerned. Cells were longer in epidermis than in the other tissues along the elongation zone of the root. 5) Roots curved at 1.5mm from the root tips directly by the longer elongation of cells in epidermis and cortex at the convex side than the other side and the curvature was supposed to be less affected by the imbalance of mitotic activity in the root tips. It was concluded that the mechanism of rotation growth of roots might be controlled by same endogenous factors where the three-dimensional imbalance of mitotic activity and probably their periodical movements could promote the asychronous elongation of cells in the tissues of epidermis, cortex and stele and a few millimeters of root tips were supposed to be viscous that could curve easily. 6) Mitotic activities in the seminal roots were examined three-dimensionally with Lolium multifiorum, Dactylis glomerata, Phleum pratense, Sorghum sudanense, Paspalum notatum, Medicago sativa, Trifolium incarnatum and Trifolium repens and it was found that, in all of the eight species examined, there were imbalances of the activity in the mitotic zone of the roots like Z. mays as mentioned elsewhere implying there might be some relations with the rotation growth of the roots in these species.